Low Emission Polyoxymethylene Composition

ABSTRACT

A polyoxymethylene polymer composition is disclosed containing a formaldehyde stabilizer package. The formaldehyde stabilizer package, which contains at least two emission control agents, dramatically and unexpectedly reduces formaldehyde emissions. The formaldehyde stabilizer package includes at least two emission control agents selected from the group of benzoguanamine compounds, a hydantoin, a substituted hydantoin, an amino acid, and an alkylene urea such as ethylene urea.

RELATED APPLICATIONS

The present application is based on and claims priority to U.S.Provisional Patent Application Ser. No. 62/483,108, having a filing dateof Apr. 7, 2017, which is incorporated herein by reference.

BACKGROUND

Polyacetal polymers, which are commonly referred to aspolyoxymethylenes, have become established as exceptionally usefulengineering materials in a variety of applications. Polyoxymethylenepolymers, for instance, are widely used in constructing molded parts,such as parts for use in the automotive industry and the electricalindustry. Polyoxymethylene polymers, for instance, have excellentmechanical properties, fatigue resistance, abrasion resistance, chemicalresistance, and moldability.

Although polyacetal resins possess many useful properties, the polymershave a tendency to degrade when heated and are inherently unstable in anoxidative atmosphere or in an acidic or alkaline environment. Inparticular, polyacetal resins have a tendency to emit formaldehydeduring processing and after the polymer has been molded into a part.Formaldehyde is not only a contaminant, but can also adversely affectmetallic components that may be placed in association with the polymer.For example, formaldehyde readily oxidizes to formic acid which cancorrode metals or cause discoloration.

In view of the above, those skilled in the art have attempted to combinepolyacetal polymers with various compounds in order to lowerformaldehyde emissions. For instance, in the past, polyacetal polymershave been combined with melamines in order to achieve lower formaldehydeemission performance. In addition, various other chemical compounds havebeen suggested for lowering formaldehyde emissions.

Although various chemical compounds used in the past have successfullylowered formaldehyde emissions from products made from polyoxymethylenepolymers, further improvements in formaldehyde emissions are needed. Forinstance, stricter government regulations continue to require furtherimprovements in reducing formaldehyde emissions.

Unfortunately, however, when additives are combined with a polyacetalpolymer in order to enhance one property, the additive may have anadverse impact on another property. For example, adding greater amountsof formaldehyde scavengers into polyoxymethylene polymer compositionscan compromise one or more properties of the polymer. For instance,excess amounts of formaldehyde scavengers may increase the occurrence ofmold deposits and/or begin to adversely affect other physicalproperties.

In view of the above, a need exists for an improved formaldehydestabilizer package capable of further reducing formaldehyde emissionswithout adversely affecting other properties of the polyoxymethylenepolymer composition.

SUMMARY

In general, the present disclosure is directed to a polymer compositioncontaining primarily a polyacetal resin and to molded products made fromthe composition. The polymer composition of the present disclosure isparticularly formulated to exhibit ultra-low formaldehyde emissions. Forexample, polyoxymethylene polymer compositions formulated in accordancewith the present disclosure can exhibit a formaldehyde emission whentested according to VDA Test 275 of less than about 5 ppm, such as lessthan about 4 ppm, such as even less than about 3 ppm. The VDA 275 Test(German Automotive Industry Recommendation No. 275) is documented byKraftfahrwesen e. V., July 1994.

In one embodiment, for instance, the polymer composition of the presentdisclosure comprises a polyoxymethylene polymer in combination with aformaldehyde stabilizer package for reducing formaldehyde emissions. Theformaldehyde stabilizer package, in one embodiment, can comprise a blendof emission control agents. The blend includes at least two emissioncontrol agents selected from a guanamine compound, a hydantoin, asubstituted hydantoin, an amino acid, and an alkylene urea such as anethylene urea. For instance, in one embodiment, the formaldehydestabilizer package may comprise a blend of a guanamine compound and asubstituted hydantoin, such as allantoin. Alternatively, theformaldehyde stabilizer package may comprise a blend of a guanaminecompound and a hydantoin. In still another embodiment, the formaldehydestabilizer package comprises a blend of a guanamine compound and anamino acid. The amino acid, for instance, may comprise arginine. Thesubstituted hydantoin, the hydantoin, or the amino acid may be presentin the polymer composition generally in an amount less than about 0.5%by weight, such as in an amount less than about 0.3% by weight, such asin an amount less than about 0.2% by weight. The above emission controlagents are generally present in the polymer composition in an amountgreater than about 0.001% by weight.

In one embodiment, the guanamine compound comprises benzoguanamine. Whenpresent, the benzoguanamine can be included in the composition in anamount greater than about 0.2% by weight, such as in an amount greaterthan about 0.3% by weight, such as in an amount greater than about 0.4%by weight and generally in an amount less than about 2% by weight, suchas in an amount less than about 1.5% by weight. The guanamine compoundcan be present in relation to another emission control agent at a weightratio of from about 20:1 to about 1:1, such as from about 15:1 to about2:1, such as from about 8:1 to about 3:1.

In an alternative embodiment, especially when the polyoxymethylenepolymer composition is used for producing medical products, theformaldehyde stabilizer package comprises a blend of a substitutedhydantoin and an amino acid. The substituted hydantoin may compriseallantoin. The amino acid may comprise arginine.

In one embodiment, the formaldehyde stabilizer package contains anethylene urea, such as in an amount from about 0.001% by weight to about5% by weight. The ethylene urea can be combined with any of the otherformaldehyde stabilizers described above including benzoguanimine and/orallantoin.

In general, any suitable polyoxymethylene polymer may be contained inthe polymer composition. In one embodiment, the polyoxymethylene polymerhas a melt flow rate of from about 5 cm³/10 min to about 15 cm³/10 min.In an alternative embodiment, the polyoxymethylene polymer has a meltflow rate of from about 18 cm³/10 min to about 40 cm³/10 min.

Various other additives may be contained in the polymer composition. Inone embodiment, for instance, the composition further contains an acidscavenger, such as a calcium salt. The composition can also contain acoloring agent. The coloring agent can be present in the composition inan amount from about 0.1% by weight to about 5% by weight. When acoloring agent is present in the composition, the acid scavenger maycomprise calcium propionate.

In one embodiment, the polymer composition contains a nucleant in anamount from about 0.05% by weight to about 1% by weight, an antioxidantin an amount from about 0.05% to about 2% by weight, and a lubricant inan amount from about 0.05% to about 1.5% by weight.

In one embodiment, the polymer composition may include an impactmodifier. The impact modifier, for instance, may comprise athermoplastic elastomer, such as a thermoplastic polyurethane elastomer.The impact modifier can be present in an amount from about 5% by weightto about 30% by weight.

The polymer composition can also contain one or more reinforcing agents.The reinforcing agent, for instance, may comprise reinforcing fibers,such as glass fibers. Reinforcing fibers can be present in the polymercomposition generally in an amount from about 3% by weight to about 40%by weight.

In one embodiment, the polymer composition can also include a UVstabilizer.

Polymer compositions made in accordance with the present disclosure canhave an excellent balance of physical properties. For instance, thepolymer composition can have a tensile modulus of at least 1200 MPa whentested according to ISO Test 527 at 23° C., can have a tensile strain atyield of greater than about 7% when tested according to ISO Test 527 at23° C., and can have a notched Charpy impact strength of greater thanabout 3 kJ/m² when tested according to ISO Test 179-1 at 23° C.

Various different and diverse articles can be molded from the polymercomposition. Due to the low formaldehyde emissions, the polymercomposition is particularly well suited to producing molded articles forthe interior of an automobile. The molded article may comprise, forinstance, a latch, a lever, a gear, a pivot housing, a decorative trimpiece, a door handle, a bracket, a speaker grill, or a seat rail.Alternatively, the polymer composition may be used to produce a medicalproduct. The medical product, for instance, may comprise an inhaler oran injector.

Other features and aspects of the present disclosure are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present disclosure is set forthmore particularly in the remainder of the specification, includingreference to the accompanying figures, in which:

FIG. 1 is a perspective view of the interior of an automobileillustrating various molded articles that may be made in accordance withthe present disclosure;

FIG. 2 is a perspective view of a medical inhaler that may be made frommolded parts in accordance with the present disclosure; and

FIG. 3 is a perspective view of a medical injector containing moldedparts made in accordance with the present disclosure.

FIG. 4 illustrates the apparatus used to measure formaldehyde emissionas described in the example below.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only and isnot intended as limiting the broader aspects of the present disclosure.

In general, the present disclosure is directed to a polymer compositioncontaining a polyacetal resin, particularly a polyoxymethylenecopolymer, that exhibits low formaldehyde emissions. The polymercomposition is well suited for use in molding processes for producingmolded articles. The polymer composition can contain one or morecoloring agents for producing molded articles having any desired color.The molded articles can be used in a limitless variety of differentapplications and in multiple fields. In one embodiment, for instance,molded articles may be made according to the present disclosure that aredesigned to function as automotive parts, such as automotive partsdesigned to be used in the interior of vehicles, such as cars andtrucks.

More particularly, the present disclosure is directed to a polymercomposition containing a polyacetal resin in combination with aformaldehyde stabilizer package. The formaldehyde stabilizer packagecomprises a blend of emission control agents. Emission control agentsthat can be used in the formaldehyde stabilizer package includeguanamine compounds, a hydantoin, a substituted hydantoin, an aminoacid, and an alkylene urea such as an ethylene urea. The guanaminecompound, for instance, may comprise a benzoguanamine.

In one embodiment, the formaldehyde stabilizer package comprises a blendof a guanamine compound and at least one of a hydantoin, a substitutedhydantoin, an amino acid, or an ethylene urea. In one embodiment, forinstance, the formaldehyde stabilizer package comprises a combination ofa guanamine compound and allantoin, which is a substituted hydantoin.Alternatively, the formaldehyde stabilizer package may comprise amixture of a guanamine compound with an amino acid, such as arginine. Insome embodiments, the formaldehyde stabilizer package dramatically andefficiently lowers formaldehyde emissions from the polymer compositionwithout compromising other properties.

For instance, in one embodiment, the polymer composition containing thepolyoxymethylene polymer exhibits a formaldehyde emission pursuant toVDA 275 of less than about 5 ppm (μg/g), such as less than about 4 ppm,such as less than about 3 ppm. The formaldehyde emission of the polymercomposition may be substantially zero.

In general, any suitable polyoxymethylene polymer may be incorporatedinto the polymer composition.

The preparation of the polyoxymethylene polymer can be carried out bypolymerization of polyoxymethylene-forming monomers, such as trioxane ora mixture of trioxane and a cyclic acetal such as dioxolane in thepresence of a molecular weight regulator, such as a glycol. Thepolyoxymethylene polymer used in the polymer composition may comprise ahomopolymer or a copolymer. According to one embodiment, thepolyoxymethylene is a homo- or copolymer which comprises at least 50mol. %, such as at least 75 mol. %, such as at least 90 mol. % and suchas even at least 97 mol. % of —CH₂O-repeat units.

In one embodiment, a polyoxymethylene copolymer is used. The copolymercan contain from about 0.01 mol. % to about 20 mol. % and in particularfrom about 0.5 mol. % to about 10 mol. % of repeat units that comprise asaturated or ethylenically unsaturated alkylene group having at least 2carbon atoms, or a cycloalkylene group, which has sulfur atoms or oxygenatoms in the chain and may include one or more substituents selectedfrom the group consisting of alkyl cycloalkyl, aryl, aralkyl,heteroaryl, halogen or alkoxy. In one embodiment, a cyclic ether oracetal is used that can be introduced into the copolymer via aring-opening reaction.

Preferred cyclic ethers or acetals are those of the formula:

in which x is 0 or 1 and R² is a C₂-C₄-alkylene group which, ifappropriate, has one or more substituents which are C₁-C₄-akyl groups,or are C₁-C₄-alkoxy groups, and/or are halogen atoms, preferablychlorine atoms. Merely by way of example, mention may be made ofethylene oxide, propylene 1,2-oxide, butylene 1,2-oxide, butylene1,3-oxide, 1,3-dioxane, 1,3-dioxolane, and 1,3-dioxepan as cyclicethers, and also of linear oligo- or polyformals, such as polydioxolaneor polydioxepan, as comonomers. It is particularly advantageous to usecopolymers composed of from 99.5 to 95 mol. % of trioxane and of from0.01 to 5 mol. %, such as from 0.5 to 4 mol. %, of one of theabove-mentioned comonomers. In one embodiment, the polyoxymethylenepolymer contains relatively low amounts of comonomer. For instance, thecomonomer can be present in an amount less than about 2 mol. %, such asless than about 1.5 mol. %, such as less than about 1 mol. %, such asless than about 0.8 mol. %, such as less than about 0.6 mol. %.

The polymerization can be effected as precipitation polymerization or inthe melt. By a suitable choice of the polymerization parameters, such asduration of polymerization or amount of molecular weight regulator, themolecular weight and hence the MVR value of the resulting polymer can beadjusted.

In one embodiment, the polyoxymethylene polymer used in the polymercomposition may contain a relatively high amount of reactive groups orfunctional groups in the terminal positions. The reactive groups, forinstance, may comprise —OH or —NH₂ groups.

In one embodiment, the polyoxymethylene polymer can have terminalhydroxyl groups, for example hydroxyethylene groups and/or hydroxyl sidegroups, in at least more than about 50% of all the terminal sites on thepolymer. For instance, the polyoxymethylene polymer may have at leastabout 70%, such as at least about 80%, such as at least about 85% of itsterminal groups be hydroxyl groups, based on the total number ofterminal groups present. It should be understood that the total numberof terminal groups present includes all side terminal groups.

In one embodiment, the polyoxymethylene polymer has a content ofterminal hydroxyl groups of at least 15 mmol/kg, such as at least 18mmol/kg, such as at least 20 mmol/kg. In one embodiment, the terminalhydroxyl group content ranges from 18 to 50 mmol/kg. In an alternativeembodiment, the polyoxymethylene polymer may contain terminal hydroxylgroups in an amount less than 20 mmol/kg, such as less than 18 mmol/kg,such as less than 15 mmol/kg. For instance, the polyoxymethylene polymermay contain terminal hydroxyl groups in an amount from about 5 mmol/kgto about 20 mmol/kg, such as from about 5 mmol/kg to about 15 mmol/kg.For example, a polyoxymethylene polymer may be used that has a lowerterminal hydroxyl group content but has a higher melt volume flow rate.

In addition to or instead of the terminal hydroxyl groups, thepolyoxymethylene polymer may also have other terminal groups usual forthese polymers. Examples of these are alkoxy groups, formate groups,acetate groups or aldehyde groups. According to one embodiment, thepolyoxymethylene is a homo- or copolymer which comprises at least 50mol-%, such as at least 75 mol-%, such as at least 90 mol-% and such aseven at least 95 mol-% of —CH₂O-repeat units.

In one embodiment, a polyoxymethylene polymer can be produced using acationic polymerization process followed by solution hydrolysis toremove any unstable end groups. During cationic polymerization, aglycol, such as ethylene glycol or methylal can be used as a chainterminating agent. A heteropoly acid, triflic acid or a boron compoundmay be used as the catalyst.

The polyoxymethylene polymer can have any suitable molecular weight. Themolecular weight of the polymer, for instance, can be from about 4,000grams per mole to about 20,000 g/mol. In other embodiments, however, themolecular weight can be well above 20,000 g/mol, such as from about20,000 g/mol to about 100,000 g/mol.

The polyoxymethylene polymer present in the composition can generallyhave a melt flow index (MFI) ranging from about 0.1 to about 80 cm³/10min, as determined according to ISO 1133 at 190° C. and 2.16 kg. In oneembodiment, the polyoxymethylene polymer may have a melt flow index offrom about 5 cm³/10 min to about 15 cm³/10 min, such as from about 8cm³/10 min to about 12 cm³/10 min. In an alternative embodiment, apolyoxymethylene polymer may be used that has a relatively high meltflow index. For instance, the polyoxymethylene polymer may have a meltflow index of from about 18 cm³/10 min to about 40 cm³/10 min, such asfrom about 20 cm³/10 min to about 35 cm³/10 min.

Suitable commercially available polyoxymethylene polymers are availableunder the trade name Hostaform® (HF) by Celanese.

The polyoxymethylene polymer may be present in the polyoxymethylenepolymer composition in an amount of at least 50 wt. %, such as at least60 wt. %, such as at least 70 wt. %, such as at least 80 wt. %, such asat least 85 wt. %, such as at least 90 wt. %, such as at least 93 wt. %.In general, the polyoxymethylene polymer is present in an amount of lessthan about 100 wt. %, such as less than about 99 wt. %, such as lessthan about 97 wt. %, wherein the weight is based on the total weight ofthe polyoxymethylene polymer composition.

The polyoxymethylene polymer as described above is combined with aformaldehyde stabilizer package that dramatically and efficientlyreduces formaldehyde emissions from the polymer composition. Theformaldehyde stabilizer package of the present disclosure comprises ablend of emission control agents. For instance, the blend includes atleast two emission control agents selected from the group includingguanamine compounds, a hydantoin, a substituted hydantoin, an aminoacid, and an alkylene urea such as an ethylene urea.

In one embodiment, the formaldehyde stabilizer package contains aguanamine compound. The guanamine compound may include an aliphaticguanamine-based compound, an alicyclic guanamine-based compound, anaromatic guanamine-based compound, a hetero atom-containingguanamine-based compound, or the like. In one embodiment, the guanaminecompound comprises a benzoguanamine. When included in the composition,the guanamine compound can be present in the polymer composition in anamount of at least about 0.05% by weight, such as in an amount of atleast about 0.1% by weight, such as in an amount of at least about 0.3%by weight, such as in an amount of at least about 0.5% by weight. Theguanamine compound is generally present in the composition in an amountless than about 2% by weight, such as in an amount less than about 1.5%by weight, such as in an amount less than about 1% by weight, such asless than about 0.8% by weight.

The formaldehyde stabilizer package may also include hydantoin or asubstituted hydantoin. One example of a substituted hydantoin isallantoin. Allantoin is also known as (2,5-dioxo-4-imidazolidinyl) ureaand has the chemical formula C₄H₆N₄O₃. Allantoin has been found toreduce formaldehyde emissions even when one or more light stabilizersare present in the composition. When included in the composition,hydantoin or a substituted hydantoin may be present generally in anamount less than about 1.5% by weight, such as in an amount less thanabout 1% by weight, such as in an amount less than about 0.5% by weight,such as in an amount less than about 0.3% by weight, such as in anamount less than about 0.2% by weight. The hydantoin or substitutedhydantoin can generally be present in an amount greater than about0.001% by weight.

The formaldehyde stabilizer package may also contain an amino acid inconjunction with at least one of the other emission control agents. Theamino acid, for instance, may comprise an α-amino acid, a β-amino acid,a γ-amino acid, a δ-amino acid, and mixtures thereof. For instance, theamino acid may comprise a monoaminomonocarboxylic acid or amonoaminodicarboxylic acid. Examples include glycine, alanine, valine,norvaline, leucine, norleucine, isoleucine, phenylalanine, tyrosine,diiodotyrosine, surinamine, threonine, serine, proline, hydroxyproline,tryptophan, methionine, cystine, cysteine, citrulline, α-aminobutyricacid, hexahydropicolinic acid, teanine, aspartic acid, glutamic acid,asparagine, glutamine, hexahydrodipicolinic acid, hexahydroquinolinicacid, and mixtures thereof. Other amino acids that may be used includediaminomonocarboxylic acids such as lysine, hydroxylysine, arginine,histidine, or mixtures thereof. One amino acid particularly well suitedfor use in the present disclosure, for instance, is arginine. Argininecan be considered an aliphatic amino acid.

When present in the composition, an amino acid can be included in anamount generally less than about 2% by weight, such as in an amount lessthan about 1.5% by weight, such as in an amount less than about 1% byweight, such as in an amount less than about 0.5% by weight, such as inan amount less than about 0.3% by weight, such as in an amount less thanabout 0.2% by weight. The amino acid is generally present in an amountgreater than about 0.001% by weight.

The formaldehyde stabilizer package of the present disclosure can bemade up of various different combinations of the emission control agentsdepending upon the particular application and the desired result. In oneembodiment, for instance, the formaldehyde stabilizer package includes aguanamine compound in combination with at least one of the otheremission control agents. For instance, the guanamine compound can becombined with allantoin and/or arginine. In one embodiment, theformaldehyde stabilizer package includes a combination of the guanaminecompound, hydantoin, a substituted hydantoin, and an amino acid.

In an alternative embodiment, the formaldehyde stabilizer package doesnot contain a guanamine compound such as benzoguanamine. For instance,the formaldehyde stabilizer package can be guanamine-free. In oneembodiment, for instance, the formaldehyde stabilizer package comprisesa combination of a substituted hydantoin, such as allantoin, and anamino acid, such as arginine. In still another embodiment, theformaldehyde stabilizer package may comprise a blend of hydantoin, asubstituted hydantoin, an amino acid, and an ethylene urea.

In one embodiment, the formaldehyde stabilizer package may also containan ethylene urea, such as 2-imidazolidone or 2-imidazolidinone. Forexample, one embodiment may contain a compound of the following formula:

The ethylene urea may be found in some embodiments in an amount greaterthan about 0.001% by weight, such as greater than about 0.01% by weight,such as greater than about 0.1% by weight, such as greater than about 1%by weight, such as greater than about 3% by weight. In some embodiments,the ethylene urea may be present in amounts less than about 5% byweight, such as less than about 3% by weight, such as less than about 1%by weight, such as less than about 0.1% by weight.

Advantageously, the ethylene urea may, in some embodiments, be combinedwith at least one other formaldehyde stabilizing compound forsynergistic effect. For instance, the ethylene urea may be combined withbenzoguanimine and/or allantoin.

In each of the formaldehyde stabilizer packages described above, thestabilizer package can include a single amino acid and/or a singlesubstituted hydantoin or at least two amino acids and/or at least twosubstituted hydantoins.

In addition to a polyoxymethylene polymer and a formaldehyde stabilizerpackage, the polymer composition of the present disclosure can containvarious other additives and ingredients. For instance, in oneembodiment, the polymer composition may contain an acid scavenger. Theacid scavenger can comprise a carboxylic acid salt.

For instance, the carboxylic acid salt may comprise a salt of a fattyacid, such as a metal salt of a fatty acid. For example, the carboxylicacid salt may comprise an alkaline earth metal salt of a fatty acid. Thecation of the salt, for instance, may comprise calcium, barium, lithium,sodium, magnesium, zinc, or the like.

The fatty acid can contain a carbon chain of generally from about 3carbon atoms to about 20 carbon atoms. The fatty acid may comprise adicarboxylic acid or a tricarboxylic acid.

In one embodiment, the metal salt of the fatty acid may comprise a metalsalt of citric acid, propionic acid, stearic acid, butanoic acid,hexanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid,and the like. In one particular embodiment, the metal salt of the fattyacid may comprise calcium propionate, calcium 12-hydroxystearate, acalcium citrate such as tricalcium citrate, and mixtures thereof. In oneembodiment, when the polyoxymethylene polymer composition includes oneor more coloring agents, various benefits and advantages are obtained bycombining the coloring agents with calcium propionate.

One or more carboxylic acid salts are generally present in the polymercomposition in an amount greater than about 0.05% by weight, such as inan amount greater than about 0.1% by weight, such as in an amountgreater than about 0.2% by weight, such as in an amount greater thanabout 0.3% by weight, such as in an amount greater than about 0.4% byweight, such as in an amount greater than about 0.5% by weight. One ormore carboxylic acid salts are generally present in the polymercomposition in an amount less than about 5% by weight, such as in anamount less than about 3% by weight, such as in an amount less thanabout 2% by weight, such as in an amount less than about 1.5% by weight,such as in an amount less than about 1% by weight.

The polymer composition of the present disclosure may also contain otherknown additives such as, for example, antioxidants, UV stabilizers orheat stabilizers, impact modifiers and/or reinforcing fibers. Inaddition, the compositions can contain processing auxiliaries, forexample adhesion promoters, lubricants, nucleants, demolding agents,fillers, or antistatic agents and additives which impart a desiredproperty to the compositions and articles or parts produced therefrom.

In one embodiment, an ultraviolet light stabilizer may be present. Theultraviolet light stabilizer may comprise a benzophenone, abenzotriazole, or a benzoate. The UV light absorber, when present, maybe present in the polymer composition in an amount of at least about0.01 wt. %, such as at least about 0.05 wt. %, such as at least about0.075 wt. % and less than about 1 wt. %, such as less than about 0.75wt. %, such as less than about 0.5 wt. %, wherein the weight is based onthe total weight of the respective polymer composition.

In one embodiment, a nucleant may be present. The nucleant may increasecrystallinity and may comprise an oxymethylene terpolymer. In oneparticular embodiment, for instance, the nucleant may comprise aterpolymer of butanediol diglycidyl ether, ethylene oxide, and trioxane.The nucleant may be present in the composition in an amount of at leastabout 0.01 wt. %, such as at least about 0.05 wt. %, such as at leastabout 0.1 wt. % and less than about 2 wt. %, such as less than about 1.5wt. %, such as less than about 1 wt. %, wherein the weight is based onthe total weight of the respective polymer composition.

In one embodiment, an antioxidant, such as a sterically hindered phenol,may be present. Examples which are available commercially, arepentaerythrityltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethyleneglycol bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate],3,3′-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionohydrazide], andhexamethylene glycolbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The antioxidantmay be present in the polymer composition in an amount of at least about0.01 wt. %, such as at least about 0.05 wt. %, such as at least about0.075 wt. % and less than about 1 wt. %, such as less than about 0.75wt. %, such as less than about 0.5 wt. %, wherein the weight is based onthe total weight of the respective polymer composition.

In one embodiment, lights stabilizers, such as sterically hinderedamines, may be present in addition to the ultraviolet light stabilizer.Hindered amine light stabilizers that may be used include oligomerichindered amine compounds that are N-methylated. For instance, hinderedamine light stabilizer may comprise a high molecular weight hinderedamine stabilizer. Other embodiments of light stabilizers include2,2,6,6-tetramethyl-4-piperidyl compounds, e.g.,bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate or the polymer of dimethylsuccinate and1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl-4-piperidine. In oneembodiment, the light stabilizer may comprise 2-(2H-benzzotriazol-2-yl)4,6-bis(1-ethyl-1-phenyl-ethyl)phenol. The light stabilizers, whenpresent, may be present in the polymer composition in an amount of atleast about 0.01 wt. %, such as at least about 0.05 wt. %, such as atleast about 0.075 wt. % and less than about 1 wt. %, such as less thanabout 0.75 wt. %, such as less than about 0.5 wt. %, wherein the weightis based on the total weight of the respective polymer composition.

In one embodiment, lubricants may be present. The lubricant may comprisea polymer wax composition. Further, in one embodiment, a polyethyleneglycol polymer (processing aid) may be present in the composition. Thepolyethylene glycol, for instance, may have a molecular weight of fromabout 1000 to about 5000, such as from about 3000 to about 4000. In oneembodiment, for instance, PEG-75 may be present. In another embodiment,a fatty acid amide such as ethylene bis(stearamide) may be present.Lubricants may generally be present in the polymer composition in anamount of at least about 0.01 wt. %, such as at least about 0.05 wt. %,such as at least about 0.075 wt. % and less than about 1 wt. %, such asless than about 0.75 wt. %, such as less than about 0.5 wt. %, whereinthe weight is based on the total weight of the respective polymercomposition.

In one embodiment, a coloring agent may be present. Coloring agents thatmay be used include any desired inorganic pigments, such as titaniumdioxide, ultramarine blue, cobalt blue, and other organic pigments anddyes, such as phthalocyanines, anthraquinnones, and the like. Othercoloring agents include carbon black or various other polymer-solubledyes. In one embodiment, a combination of coloring agents may beincluded in the polymer composition. For instance, the polymercomposition may contain titanium dioxide in combination with carbonblack. In an alternative embodiment, the coloring agents present in thepolymer composition may comprise titanium dioxide in combination with atleast one color pigment, such as a yellow pigment and a green pigmentand optionally further in combination with carbon black. The coloringagent may be present in the composition in an amount of at least about0.01 wt. %, such as at least about 0.05 wt. %, such as at least about0.1 wt. %, such as at least about 0.5 wt. %, such as at least about 0.8wt. %, such as at least about 1 wt. % and less than about 5 wt. %, suchas less than about 2.5 wt. %, such as less than about 1 wt. %, whereinthe weight is based on the total weight of the respective polymercomposition.

Fillers that may be included in the composition include glass beads,wollastonite, loam, molybdenum disulfide or graphite, and/or inorganicor organic fibers.

Reinforcing fibers which may be included in the composition are mineralfibers, such as glass fibers, polymer fibers, in particular organichigh-modulus fibers, such as aramid fibers, metal fibers, such as steelfibers, carbon fibers, natural fibers, and/or fibers from renewableresources.

These fibers may be in modified or unmodified form, e.g. provided with asizing, or chemically treated, in order to improve adhesion to thepolymer. Glass fibers are particularly preferred.

Glass fibers are provided with a sizing to protect the glass fiber, tosmooth the fiber but also to improve the adhesion between the fiber andthe matrix material. A sizing usually comprises silanes, film formingagents, lubricants, wetting agents, adhesive agents optionallyantistatic agents and plasticizers, emulsifiers and optionally furtheradditives.

Specific examples of silanes are aminosilanes, e.g.3-trimethoxysilylpropylamine,N-(2-aminoethyl)-3-aminopropyltrimethoxy-silane,N-(3-trimethoxysilanylpropyl)ethane-1,2-diamine,3-(2-aminoethyl-amino)propyltrimethoxysilane,N-[3-(trimethoxysilyl)propyl]-1,2-ethane-diamine.

Film forming agents are for example polyvinylacetates, polyesters andpolyurethanes. Sizings based on polyurethanes may be usedadvantageously.

The reinforcing fibers may be compounded into the polyoxymethylenematrix, for example in an extruder or kneader. However, the reinforcingfibers may also advantageously take the form of continuous-filamentfibers sheathed or impregnated with the polyoxymethylene moldingcomposition in a process suitable for this purpose, and then processedor wound up in the form of a continuous strand, or cut to a desiredpellet length so that the fiber lengths and pellet lengths areidentical. An example of a process particularly suitable for thispurpose is the pultrusion process.

The reinforcing fibers can be present in the molding composition in anamount ranging from 5 to 45 wt.-%, such as from 10 to 40 wt.-%, whereinthe weight is based on the total weight of the composition.

The polymer composition may further comprise an impact modifier such asa thermoplastic elastomer. Thermoplastic elastomers are materials withboth thermoplastic and elastomeric properties. Thermoplastic elastomersinclude styrenic block copolymers, polyolefin blends referred to asthermoplastic olefin elastomers, elastomeric alloys, thermoplasticpolyurethanes, thermoplastic copolyesters, and thermoplastic polyamides.

Thermoplastic elastomers well suited for use in the present disclosureare polyester elastomers (TPE-E), thermoplastic polyamide elastomers(TPE-A) and in particular thermoplastic polyurethane elastomers (TPE-U).

In one particular embodiment, a thermoplastic polyurethane elastomer isused. The thermoplastic polyurethane elastomer, for instance, may have asoft segment of a long-chain diol and a hard segment derived from adiisocyanate and a chain extender. In one embodiment, the polyurethaneelastomer is a polyester type prepared by reacting a long-chain diolwith a diisocyanate to produce a polyurethane prepolymer havingisocyanate end groups, followed by chain extension of the prepolymerwith a diol chain extender. Representative long-chain diols arepolyester diols such as poly(butylene adipate)diol, poly(ethyleneadipate)diol and poly(ε-caprolactone)diol; and polyether diols such aspoly(tetramethylene ether)glycol, poly(propylene oxide)glycol,poly(ethylene oxide)glycol, polycarbonate diol and/or a polyesterpolycarbonate diol. Suitable diisocyanates include4,4′-methylenebis(phenyl isocyanate), 2,4-toluene diisocyanate,1,6-hexamethylene diisocyanate and4,4′-methylenebis-(cycloxylisocyanate). Suitable chain extenders areC₂-C₆ aliphatic diols such as ethylene glycol, 1,4-butanediol,1,6-hexanediol and neopentyl glycol. One example of a thermoplasticpolyurethane is characterized as essentially poly(adipicacid-co-butylene glycol-co-diphenylmethane diisocyanate).

The amount of thermoplastic elastomer contained in the polymercomposition can vary depending upon various factors. For instance, thethermoplastic elastomer can be present in an amount ranging from about0.5% by weight to about 50% by weight. In one embodiment, for instance,a thermoplastic elastomer or impact modifier may be present in thecomposition in an amount less than about 25% by weight, such as in anamount less than about 15% by weight, such as in an amount less thanabout 10% by weight. The thermoplastic elastomer or impact modifier isgenerally present in an amount greater than about 2% by weight, such asin an amount greater than about 5% by weight, such as in an amountgreater than about 8% by weight, such as in an amount greater than about10% by weight.

In one embodiment, when an impact modifier or thermoplastic elastomer ispresent in the composition, the composition can also include a couplingagent. The coupling agent may comprise a polyisocyanate, such as adiisocyanate or triisocyanate. The coupling agent can be presentgenerally in an amount from about 0.1% to about 2% by weight, such asfrom about 0.1% to about 1% by weight.

The compositions of the present disclosure can be compounded and formedinto a polymer article using any technique known in the art. Forinstance, the respective composition can be intensively mixed to form asubstantially homogeneous blend. The blend can be melt kneaded at anelevated temperature, such as a temperature that is higher than themelting point of the polymer utilized in the polymer composition butlower than the degradation temperature. Alternatively, the respectivecomposition can be melted and mixed together in a conventional single ortwin screw extruder. Preferably, the melt mixing is carried out at atemperature ranging from 100 to 280° C., such as from 120 to 260° C.,such as from 140 to 240° C. or 180 to 220° C.

After extrusion, the compositions may be formed into pellets. Thepellets can be molded into polymer articles by techniques known in theart such as injection molding, thermoforming, blow molding, rotationalmolding and the like.

The polymer composition of the present disclosure can be used to producevarious molded parts. The parts can be formed through any suitablemolding process, such as an injection molding process or through a blowmolding process. Polymer articles that may be made in accordance withthe present disclosure include knobs, door handles, automotivedecorative trim pieces, and the like without limitation. Other polymerarticles, for instance, that may be made in accordance with the presentdisclosure include latches, levers, gears, pivot housings, speakergrills, and the like.

For instance, referring to FIG. 1, an automotive interior is shownillustrating various automotive parts that may be made in accordancewith the present disclosure. The polymer composition, for instance, maybe used to produce automotive part 10, which comprises at least aportion of an interior door handle. The polymer composition may also beused to produce a part on the steering column such as automotive part12. In general, the polymer composition can be used to mold any suitabledecorative trim piece or bezel, such as trim piece 14.

As described above, in one embodiment, the formaldehyde stabilizerpackage does not include a guanamine compound. Instead, the formaldehydestabilizer package can include a combination of a hydantoin, asubstituted hydantoin, an amino acid, and/or an ethylene urea.Guanamine-free compositions are particularly well suited for use inproducing medical products. For instance, referring to FIG. 2, aninhaler 20 is shown. The inhaler 20 includes a housing 22 attached to amouthpiece 24. In operative association with the housing 22 is a plunger26 for receiving a canister containing a composition to be inhaled. Thecomposition may comprise a spray or a powder.

During use, the inhaler 20 administers metered doses of a medication,such as an asthma medication to a patient. The asthma medication may besuspended or dissolved in a propellant or may be contained in a powder.When a patient actuates the inhaler to breathe in the medication, avalve opens allowing the medication to exit the mouthpiece. Inaccordance with the present disclosure, the housing 22, the mouthpiece24 and the plunger 26 can all be made from a polymer composition asdescribed above.

Referring to FIG. 3, another medical product that may be made inaccordance with the present disclosure is shown. In FIG. 3, a medicalinjector 30 is illustrated. The medical injector 30 includes a housing32 in operative association with a plunger 34. The housing 32 may sliderelative to the plunger 34. The medical injector 30 may be springloaded. The medical injector is for injecting a drug into a patienttypically into the thigh or the buttocks. The medical injector can beneedleless or may contain a needle. When containing a needle, the needletip is typically shielded within the housing prior to injection.Needleless injectors, on the other hand, can contain a cylinder ofpressurized gas that propels a medication through the skin without theuse of a needle. In accordance with the present disclosure, the housing32 and/or the plunger 34 can be made from a polymer composition asdescribed above.

While the polyoxymethylene polymer composition and polymer articlesproduced therefrom of the present disclosure provide improved emissionproperties, the compositions and articles may also exhibit excellentmechanical properties (ISO Test 527). For example, when tested accordingto ISO Test No. 527, the polymer composition may have a tensile modulusof greater than about 1,200 MPa, such as greater than about 2,000 MPa.The tensile modulus is generally less than about 10,000 MPa.

The polymer composition can exhibit a notched Charpy impact strength at23° C. (ISO Test 179-1) of greater than about 3 kJ/m², such as greaterthan about 6 kJ/m². The notched Charpy impact strength is generally lessthan about 20 kJ/m².

The present disclosure may be better understood with reference to thefollowing example.

EXAMPLES

The following examples were conducted in order to demonstrate some ofthe advantages and benefits of polymer compositions made according tothe present disclosure.

Example 1

Various polymer compositions were formulated, molded into testspecimens, and tested for formaldehyde emission. The polymercompositions contained an oxymethylene copolymer. The polyoxymethylenepolymer had a melt volume rate of about 9 cm³/10 min according to ISOTest 1133. In addition to the polyoxymethylene polymer, the polymercomposition contained 0.25% by weight of a nucleant, 0.3% by weight ofan antioxidant (unless otherwise noted, pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)), 0.18% byweight of a lubricant, and 0.07% by weight of calcium 12hydroxystearate. In addition, the polymer compositions all contained 1%by weight of a black color concentrate.

Various different additives were then combined with the above polymercomposition and tested for formaldehyde emission. Each formulation wascompounded on a 32 mm co-rotating twin-screw extruder (ZSK 32, Coperion,Germany). The test plaques were injection molded.

In the initial set of tests, formaldehyde emission was tested similar toa 2011 China Government Test having Test No. GB/T27630-2011. However,instead of using a Tedlar bag sampling method to capture and assessformaldehyde emission, a fixed volume chamber was used. As used herein,this test will be referred to as the “Modified GB/T27630-2011 Test” andthe procedure is as follows:

Modified GB/T27630-2011 Test Sample Considerations:

Samples are POM plaques (54×79 mm) molded according to VDA275specifications. Two plaques are used for each measurement. Plaques areconditioned for a 24±2 hours at 23° C. and 50% RH prior to analysis.Samples are analyzed within 15 days of molding.

Formaldehyde Collection Setup:

The collection apparatus is shown in FIG. 4. A 2 liter collection vesselis heated to between 145-160° C. via a heating mantle. Two POM plaquesare suspended by a wire hook and separated via a Teflon spacer. Thetemperature at the center of the plaques is 65° C. with 10° C. variationacross the length of the vertical dimension. During testing the vesselis purged with nitrogen at a rate of 500 mL/min. The gas enters the topof the vessel and exits through a DNPH-derivatized cartridge at thedistal end of the gas flow path. Formaldehyde emissions are collectedfor a period of 2 hours, followed by removal of the plaques and a 30minute purge prior to the next test. The formaldehyde-DNPH cartridge isthen washed with 5 mL of acetonitrile and analyzed via HPLC using theparameters listed below. Quantitation was performed using a commerciallyavailable mixture of 13 DNPH-derivatized aldehydes and ketones(Cerilliant) including formaldehyde-DNPH. Standards from 0.03 to 15μg/mL were fit with linear regressions (R²>0.9999).

LC Experimental Conditions:

-   -   System: Dionex Ultimate 3000; LC4    -   Column: Phenomenex Kinetex C18 2.1×100 mm, 2.6 μm SN #:        H15-038929    -   Column Temperature 40° C.    -   Injection Volume 2 μL    -   Flow Rate 0.400 m L/m in    -   Detector Wavelength 365 nm    -   Detector bandwidth 10 nm

HPLC Mobile Phase Gradient Time ACN + 0.07% TFA Water + 0.07% TFA (min)(%) (%) 0 30 70 11 42 58 12 70 30 13.5 70 30 13.6 30 70 18.8 30 70

Blanks and Controls:

An unused DNPH capture cartridge was analyzed directly via HPLC withoutany exposure to the exposure vessels. This blank test resulted in nopeak, confirming a zero background with just the DNPH cartridge. Acontrol run was also performed by running the method as normal butwithout any sample plaques and following a vessel purge. The resultantpeak was 0.12% the area of that observed for a typical plaque. Thisindicates the 30 minute purge is effective at removing emissions fromthe reactor vessel.

Three commercial formulations were also tested. The first two commercialformulations (Control 1 and Control 2) contained 0.5% by weightbenzoguanamine. The chemical composition of the third commercial samplewas unknown. The following compositions were tested and the followingresults were obtained:

TABLE 1 Formaldehyde emission Formaldehyde scavengers (μg/g) Control 1Benzoguanamine 0.5% 2.57 Control 2 Benzoguanamine 0.5% 2.46 Control 30.21 Sample 1 Melamine 0.07% 3.93 Sample 2 dicyandiamide 0.03% 11.86Sample 3 sebacic dihydrazide 0.05% 10.91 Sample 4 Allantoin 0.05% 5.97Sample 5 copolyamide 0.15% 10.89 Sample 6 Hydantoin 0.1% 4.90 Sample 7Arginine 0.03% 8.99 Sample 8 Benzoguanamine 0.5%, 2.13 Melamine 0.07%Sample 9 Benzoguanamine 0.5%, 2.26 dicyandiamide 0.03% Sample 10Benzoguanamine 0.5%, 1.74 sebacic dihydrazide 0.05% Sample 11Benzoguanamine 0.5%, 0.67 Allantoin 0.05% Sample 12 Benzoguanamine 0.5%,2.13 copolyamide 0.15% Sample 13 Benzoguanamine 0.5%, 1.25 Hydantoin0.1% Sample 14 Benzoguanamine 0.5%, 1.04 Arginine 0.03%

As shown above, Sample Nos. 11, 13 and 14 demonstrated dramaticreductions in formaldehyde emissions, especially in comparison tocompositions only containing a guanamine compound.

Further polyoxymethylene polymer compositions were then formulated andtested using the same formaldehyde emission test with benzoguanamine(BZG), arginine (ARG), and allantoin (ALT). The following results wereobtained:

TABLE 2 Formaldehyde emission Scavengers (μg/g) Control 1 BZG 0.5% 2.57Sample 15 BZG 0.6% 1.84 Sample 16 BZG 0.5%, ALT 0.1% 0.19 Sample 17 ALT0.1% 1.42 Sample 18 BZG 0.5%, ARG 0.1% 0.28 Sample 19 ARG 0.1% 1.11

Further polyoxymethylene polymer compositions were then formulatedcontaining the combination of benzoguanamine and allantoin. In addition,two different acid scavengers were tested. Specifically, calciumpropionate was tested in addition to calcium 12 hydroxystearate.

The compositions were then tested for formaldehyde emission usingdifferent tests and tested for total volatile organic compounds. Thephysical properties of the formulations were also tested. The first testfor formaldehyde emissions was as described above. The second test forformaldehyde emissions was conducted according to VDA Test 275. The testfor total volatile organic compounds (TVOC) was conducted similar to thefirst formaldehyde emission test using a fixed volume chamber. Theoutgas from the chamber, however, was sent to a Tenac cartridge andanalyzed by GC-MS.

Tensile module, tensile stress at yield, and tensile strain at yieldwere all tested according to ISO Test 527 at 23° C. Notched Charpyimpact strength was measured at 23° C. according to ISO Test 179-1.

For purposes of comparison, two controls were also tested. Control 1 wasthe same as in Table 1 above and contained 0.5% benzoguanamine. Control4, on the other hand, was a commercial product whose composition isunknown. The following results were obtained:

TABLE 3 Tensile Tensile Modified Tensile Stress Strain Notched GB TestVDA 275 TVOC Modulus at yield at yield Charpy Composition 1 (μg/g)(μg/g) (μg/g) (MPa) (MPa) (%) (kJ/m²) Control 1 BZG 0.5% 2.15 0.80 0.532584 64 10 7.0 Control 4 1.14 1.47 0.33 2525 61 10 6.2 Sample 16 BZG0.5%, 0.1 0.59 0.29 2529 64 10 7.1 ALT 0.1%, Ca 12 Hydroxy Stearate0.07% Sample 20 BZG 0.5%, 0.16 0.74 0.33 2564 64 10 6.4 ALT 0.1%, Capropionate 0.07% Sample 18 BZG 0.5%, 0.2 0.27 0.34 2600 64 10 6.4 ARG0.1%, Ca 12 Hydroxy Stearate 0.07% Sample 21 BZG 0.5%, 0.27 0.38 0.292598 64 10 6.4 ARG 0.1%, Ca propionate 0.07%

During the test, it was noticed that the calcium propionate acidscavenger was more compatible with the coloring agent, a 1% black colorconcentrate, than the calcium 12 hydroxystearate.

Example 2

Further tests were conducted with formulations made in accordance withthe present disclosure. The tests were the same as described in Example1 above. In this example, the polyoxymethylene polymer had a higher meltflow rate. Specifically, the polyoxymethylene polymer had a melt flowrate of 27 cm³/10 min. The compositions are otherwise the same as inExample 1, except a UV stabilizer was used at 0.4%, a lubricant was usedat 0.5%, and calcium propionate was substituted for calcium 12hydroxystearate. Control 5, however, used 0.05% tricalcium citrateinstead of the calcium propionate and 0.2% lubricant instead of 0.18%lubricant.

In this test, different color agent packages were incorporated into thepolymer compositions and different hindered amine light stabilizers wereused (HAL) at 0.5%. The formulations were compared to Control 5 whichcontained the same polyoxymethylene polymer in combination with 0.5% byweight benzoguanamine. Control 5 and Sample 22 were produced on atwin-screw and Samples 23 through 28 were produced on a single-screwcompounder. The following results were obtained:

TABLE 4 Modified Formaldehyde Scavengers GB Test VDA275 TVOC and ColorPackage (μg/g) (μg/g) (μg/g) Control 5 BZG 0.5%, 2.58 1.08 0.20 1% BlackSample 22 BZG 0.5%, 0.59 0.86 0.20 ALT 0.1% Black Sample 23 BZG 0.5%,0.14 0.57 0.76 ALT 0.1% Natural Sample 24 BZG 0.5%, 0.18 0.60 0.87 ALT0.1%, Tan Sample 25 BZG 0.5%, 0.17 0.59 0.43 ARG 0.1%, GRAY Sample 26BZG 0.5%, ARG 0.1%, 0.15 0.57 0.44 GRAY, Alternate HAL-1 Sample 27 BZG0.5%, ARG 0.1%, 0.17 0.67 0.47 GRAY, Alternate HAL-2 Sample 28 BZG 0.5%,0.16 0.65 0.31 ARG 0.1%, Black

Example 3

Further compositions were tested using the same base resin and additivesas in Example 1. Table 5 shows additional results of the synergisticeffect of arginine (ARG) and benzoguanamine (BZG) on the emissionperformance of POM. Control 6 is composed of 0.5% benzoguanamine.Samples 29, 30, and 31 are composed of arginine alone, a combination ofarginine and benzoguanamine, and benzoguanamine alone, respectively, atthe same loading level, i.e. 0.6%. Combination of 0.1% arginine and 0.5%benzoguanamine shows significantly lower formaldehyde (FA) emissions byboth the Modified GB and VDA275 methods, as well as the TVOC emission,than the arginine alone or benzoguanamine alone samples. This indicatesthat there is a synergistic effect between arginine and benzoguanaminein formaldehyde scavenging. Compared to the control, the 0.1% arginineand 0.5% benzoguanamine combination demonstrated approximately 5.8 timesimprovement in formaldehyde emission by the modified GB Test, 2 timesimprovement by VDA275 methods, and approximately 11 times improvement inTVOC emission.

TABLE 5 Modified GB Test VDA275 TVOC Composition (μg/g) (μg/g) (μg/g)Control 6 ARG 0%, BZG 0.5% 1.73 0.72 2.30 Sample 29 ARG 0.6%, BZG 0%1.16 0.48 1.10 Sample 30 ARG 0.1%, BZG 0.5% 0.30 0.36 0.21 Sample 31 ARG0%. BZG 0.6% 0.90 0.49 0.17

Example 4

Further compositions were tested using the same base resin and additivesas in Example 1. Table 6 shows an example combination of allantoin (ALT)and arginine and its emission performance. Control 7 is a POM samplewithout an formaldehyde scavenger such as benzoguanamine, allantoin, orarginine. Sample 32 includes the combination of 0.1% allantoin and 0.1%arginine. By adding the combination of 0.1% allantoin and 0.1% arginineto the POM of Control 7, the formaldehyde emissions were reduced byapproximately 145 times via the Modified GB Test and 26 times viaVDA275. This is also approximately 25 times better by the Modified GBTest and 1.1 times better by VDA275, in formaldehyde emission, thanControl 6.

TABLE 6 Modified GB Test VDA275 Composition (μg/g) (μg/g) Control 7 Noformaldehyde scavenger added 10.19 17.31 Control 6 ARG 0%, BZG 0.5% 1.730.72 Sample 32 ALT 0.1%, ARG 0.1% 0.07 0.66

Benzoguanamine may not be suitable for use in some applications; forexample, various regulations may restrict the amount of benzoguanamineused in a particular product. In contrast, arginine (L-arginine, CAS#74-79-3) is an amino acid, and allantoin (CAS #97-59-6) is widely usedin cosmetics and pharmaceutical applications. Use of less restrictedingredients, such as allantoin and arginine, not only achieves betterperformance than existing solutions, but also could expand theapplication of low emission POM, such as to heavily regulated products.

Example 5

Further compositions were tested using the same base resin and additivesas in Example 1, except that Samples 34-36 were produced with asubstituted POM polymer having a melt volume rate of about 8 cm³/10 minaccording to ISO Test 1133, and Samples 35 and 36 contain 1% of a blackcolor concentrate. Combinations of allantoin, arginine, andbenzoguanamine were also investigated in formaldehyde emissionperformance. The following mixtures were considered: allantoin at 0%,0.075%, 0.15%, 0.225% loadings, arginine at 0%, 0.05%, 0.075%, 0.15%,0.225% loadings, benzoguanamine at 0%, 0.25%, 0.5%, 0.75% loadings, andtheir combinations. Some examples of the study are shown in Table 7.Among studied samples, the combination of 0.1% allantoin, 0.15%arginine, and 0.5% benzoguanamine (Sample 34 and Sample 36) performedbest in formaldehyde and TVOC emissions.

TABLE 7 Modified GB Test VDA275 TVOC Description Composition (μg/g)(μg/g) (μg/g) Control 6 Natural ALT 0%, 1.73 0.72 2.30 ARG 0%, BZG 0.5%Sample 33 Natural ALT 0.1%, 0.08 0.51 0.01 ARG 0.05%, BZG 0.5% Sample 34Natural ALT 0.1%, 0.02 0.05 0.01 ARG 0.15%, BZG 0.5% Sample 35 Black ALT0.1%, 0.06 0.14 0.02 ARG 0.05%, BZG 0.5% Sample 36 Black ALT 0.1%, 0.010.11 0.01 ARG 0.15%, BZG 0.5%

Both natural samples and samples tinted with a 1% mixture of a blackcolor concentrate were tested. The combination in a natural POM sampleshowed approximately 87 times lower formaldehyde emission by theModified GB Test, 15 times lower formaldehyde emission by VDA275, and230 times lower TVOC emission than Control 6. The same combination in ablack sample showed 173 times lower formaldehyde emission by theModified GB Test, 6.3 times lower formaldehyde emission by VDA275, and230 times lower TVOC emission than the control. The natural sample of0.1% allantoin, 0.15% arginine, and 0.5% benzoguanamine (Sample 34)showed a noticeable yellowness, compared to a typical unfilled POM. Theblack sample, Sample 36, can be still used because the yellowness causedby the additives is masked by black pigment.

The combination of 0.1% allantoin, 0.05% arginine, and 0.5%benzoguanamine showed the second-best formaldehyde emission scavengingperformance. Such combination in a natural sample (Sample 33) showedapproximately 22 times lower formaldehyde emission by the Modified GBTest, approximately 1.4 times lower formaldehyde by VDA275, and 230times lower TVOC compared to Control 6. The same combination in a blacksample (Sample 35) showed approximately 29 times lower formaldehydeemission by the Modified GB Test, approximately 5 times lowerformaldehyde by VDA275, and 115 times lower TVOC compared to thecontrol. Although these results are significant improvement from thecontrol, and the combinations discussed previously, these samplesdemonstrated slightly higher formaldehyde emission than 0.1% allantoin,0.15% arginine, and 0.5% benzoguanamine while being slightly yellowerthan a typical unfilled POM.

Example 6

Both the combination of 0.1% allantoin, 0.05% arginine, and 0.5%benzoguanamine and the combination of 0.1% allantoin, 0.15% arginine,and 0.5% benzoguanamine were trialed in a UV stabilized formulation,with 0.5% HAL, a phenolic UV stabilizer, and a polyethylene glycol andPOM, in gray, tan, and black colors. The emission level by the ModifiedGB Test was between 0.05 ppm to 0.1 ppm, which is a 20 to 40 timesimprovement compared to the control. The formaldehyde emission by VDA275method was improved by approximately 5 times improved from the control.

Example 7

Further compositions were tested using the same base resin and additivesas used in Sample 34 of Example 5, except that the level of antioxidantwas increased to 0.4%. In the following example, the combination of 0.1allantoin, 0.05% arginine, and 0.5% benzoguanamine was further optimizedto tone down the yellowness and to improve the emission performance ofSample 33. Some examples are shown in Table 8.

TABLE 8 Color Color Color Modified L a b GB Test VDA275 TVOC Compositionrating rating rating (μg/g) (μg/g) (μg/g) Sample 37 ALT 0.1%, 91.4 −3.1310.5 0.033 0.076 0.02 ARG 0.05%, BZG 0.5%, AO-1 0.4% Sample 38 ALT 0.1%,94.4 −5.98 6.42 0.019 0.056 0.02 ARG 0.05%, BZG 0.5%, AO-2 0.4%,brightener 0.01% Sample 39 ALT 0.1%, 94.8 −5.68 4.56 0.021 0.066 0.02ARG 0.05%, BZG 0.5%, AO-1 0.4%, brightener 0.01% Sample 56 ALT 0.1%,91.90 −2.66 8.11 0.015 0.037 — ARG 0.05%, BZG 0.5%, AO-2 0.4%, No Ca12hydroxystearate

In Sample 37, the antioxidant (AO) loading was increased to 0.4% in thisstudy, compared to Sample 33. The formaldehyde emission of Sample 37reduced by approximately 2.4 times by the Modified GB Test and 6.7 timesby VDA275 compared to Sample 33. In Sample 38 and Sample 39, the sameantioxidant loading level was also used, and both samples included anoptical brightener (OB) at 0.01% loading. Sample 38 used AO-2(ethylenebis(oxyethylene)bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate))and Sample 39 used AO-1 (pentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)) as anantioxidant.

Sample 38 and Sample 39 demonstrated similar emission levels slightlyimproved from Sample 37. When an optical brightener was used, theyellowness of the 0.1% allantoin, 0.05% arginine, and 0.5%benzoguanamine combination was improved, as indicated by the ‘b’ ratingof LAB color measurement.

However, after 1000 hours of exposure to fluorescent light, the colorshift of Sample 38 and Sample 39 was noticeable as the opticalbrightener loses its effect. Sample 56 was yellower than Sample 38 andSample 39 to start with, but the color does not shift because there isno optical brightener. The formaldehyde emission performance of Sample56 was significantly improved. Sample 56 has an acceptable yellowness,although not the best, and great formaldehyde emission performance, andmay be used as a general purpose, medium flow, extreme low emission POM.

Example 8

Some scavenger packages, such as those that may use 0.5% benzoguanamine,are not generally used in some grades of POM, such as those in which animpact modifier thermoplastic polyurethane (TPU) is conjugated to POM.It is believed that benzoguanamine may, in some cases, interfere thecoupling reaction of TPU and POM. In order to achieve lower formaldehydeemission in such POM grades, a higher antioxidant loading has been used.The possibility of using the combination of allantoin and arginine insuch grades was studied by representing said grades by Control 8, asshown in Table 9. Control 9 is the low emission version of Control 8,achieved not by 0.5% benzoguanamine but by 0.5% antioxidant loading.Unless otherwise noted, the compositions include 18% TPU, 0.2%antioxidant, 0.15% lubricant, 0.5% diisocyanate coupling agent, and thebalance percentage of POM resin.

When either allantoin or arginine was used alone at 0.1%, theformaldehyde emission was significantly reduced compared to thecontrols. When the combination of allantoin and arginine was used, theformaldehyde reduction was remarkable. The combination of 0.05%allantoin and 0.05% arginine (Sample 42) demonstrated almost a half offormaldehyde emission level compared to allantoin alone or argininealone at 0.1% loading, which indicates the synergistic effect of theallantoin and arginine combination. The combination of 0.075% allantoinand 0.075% arginine (Sample 43), showed 80 times reduced formaldehydeemission by the Modified GB Test, and approximately 9.4 times reducedformaldehyde emission by VDA275.

TABLE 9 Modified GB Test VDA275 TVOC Composition (μg/g) (μg/g) (μg/g)Control 8 No FA scavenger 4.97 1.995 0.31 Control 9 No FA scavenger,AO-1 3.19 1.231 0.41 0.5% Sample 40 ALT 0.1%, ARG 0% 0.14 0.540 0.39Sample 41 ALT 0%, ARG 0.1% 0.12 0.120 0.49 Sample 42 ALT 0.05%, ARG0.05% 0.06 0.163 0.34 Sample 43 ALT 0.075%, ARG 0.075% 0.04 0.131 1.52

Example 9

The efficacy of ethylene urea (EU) as a formaldehyde scavenger wasevaluated using a 0.1% loading of ethylene urea in POM compositionsusing the same base resin and additives as used in Sample 34 of Example5. Table 10 shows the formaldehyde emission results of adding 0.1%ethylene urea of 3 different hydration and purities to POM. As shown inTable 10, ethylene urea was greatly effective in reducing theformaldehyde emission at 0.1% loading. By the modified GB Test method,the formaldehyde emission of a 99% purity hemihydrate ethylene ureacontaining sample (Sample 44) was approximately 12 times lower thanControl 10. By the VDA275 method, the formaldehyde emission of the samesample was approximately 2.5 times lower than Control 10. When Sample 44and Sample 46 are compared, the formaldehyde emission appears lower whena hemihydrate was used than an anhydrous; however, they both areeffective in formaldehyde scavenging. Without wishing to be bound by anyparticular theory, hydration may help the nitrogen of ethylene ureabecome more electrophilic to accept formaldehyde.

TABLE 10 Modified GB Test VDA275 Composition (μg/g) (μg/g) Control 10 Noformaldehyde scavenger 0.948 0.917 Sample 44 0.1% EU (hemihydrate 99%)0.076 0.358 Sample 45 0.1% EU (hemihydrate 87%) 0.079 0.536 Sample 460.1% EU (anhydrous 96%) 0.094 0.421

Example 10

Further examples were conducted to investigate the efficacy of ethyleneurea as a formaldehyde scavenger in the presence of other scavengers inPOM compositions using the same base resin and additives as used inSample 34 of Example 5. The ethylene urea used in this example was inhemihydrate form at 99% purity. Sample 55 substituted the antioxidantfor 0.4% AO-2 and omitted the calcium 12 hydroxystearate.

Table 11 shows some example combinations of formaldehyde scavengers andresults. It appears that the addition of ethylene urea helps reduce theformaldehyde emission level significantly, for example, as compared tothe result of its counterpart itself. When all four formaldehydescavengers are all used, the best emission performance was achieved(Sample 49). However the yellowness of Sample 49 was significant.

Sample 55 is similar to Sample 56, but 0.05% arginine was replaced with0.05% ethylene urea. The formaldehyde emission performance of Sample 55was similar to that of Sample 56 by the Modified GB Test, but almosttwice high by VDA275. This may be because arginine is especiallyeffective in scavenging under the VDA275 emission testing conditions.However, it was noted that Sample 55 showed significantly betterperformance in color: its yellowness was comparable to the sample withno formaldehyde scavengers (Sample 47). It seems that the ethylene urealoading level in Sample 55 can be further optimized to achieve thesimilar formaldehyde emission level of Sample 38, 39 or 56, withoutcompromising the yellowness.

TABLE 11 Modified Color Color Color GB Test VDA275 L a b Composition(μg/g) (μg/g) rating rating rating Sample 47 ALT 0%, ARG 0%, BZG 0%, EU0% 0.948 0.174 92.4 −0.39 1.53 Sample 48 ALT 0%, ARG 0%, BZG 0.5%, EU0.1% 0.050 0.083 92.2 −0.67 2.10 Sample 49 ALT 0.1%, ARG 0.1%, BZG 0.5%,EU 0.1% 0.011 0.045 91.1 −3.20 12.8 Sample 50 ALT 0%, ARG 0.1%, BZG 0%,EU 0.1% 0.049 0.038 91.3 −2.08 8.86 Sample 51 ALT 0.1%, ARG 0%, BZG 0%,EU 0.1% 0.051 0.164 92.20 −2.21 5.69 Sample 52 ALT 0.1%, ARG 0%, BZG0.5%, EU 0% 0.028 0.150 91.90 −2.21 5.42 Sample 53 ALT 0.1%, ARG 0.1%,BZG 0%, EU 0% 0.014 0.057 91.60 −3.19 11.2 Sample 54 ALT 0%, ARG 0.1%,BZG 0.5%, EU 0% 0.031 0.063 91.70 −1.96 7.03 Sample 55 ALT 0.1%, BZG0.5%, EU 0.05% 0.017 0.080 92.40 −0.74 1.24

Example 11

Further tests were conducted to characterize the efficacy of ethyleneurea in combination with other formaldehyde scavengers.

Samples were prepared as follows. Control 11 and Samples 57-60 containeda polyoxymethylene polymer 1 (POM-1) having a dissolved oxygen contentof 5.6%. Control 12 and Samples 61-64 contained a polyoxymethylenepolymer 2 (POM-2) having a dissolved oxygen content of 2.8%. POM-2, inparticular, has a melt flow rate of 2.2 cm³/10 min measured according toISO 1133.

Control 12 and Samples 61-64 also contained 4.5% of a polyethylene-basedacrylonitrile-styrene copolymer.

Each sample and control included 0.25% of a polyoxymethylene terpolymeras a nucleant, ethylene bis(oxyethylene)bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate) as an antioxidant(AO), 0.2% ethylene bis(stearamide), and 0.05% tricalcium citrate.

Additional additives were included in the amounts shown in Table 12.

TABLE 12 Composition Control 11 AO 0.25%, BZG 0.5% Control 12 AO 0.3%,BZG 0.5% Sample 57 AO 0.25%, EU 0.1% Sample 58 AO 0.25%, BZG 0.5%, EU0.1% Sample 59 AO 0.25%, EU 0.1%, ALT 0.1% Sample 60 AO 0.25%, BZG 0.5%,EU 0.1%, ALT 0.1% Sample 61 AO 0.3%, EU 0.1% Sample 62 AO 0.3%, BZG0.5%, EU 0.1% Sample 63 AO 0.3%, EU 0.1%, ALT 0.1% Sample 64 AO 0.3%,BZG 0.5%, EU 0.1%, ALT 0.1%

Results of the tests are provided in Table 13.

TABLE 13 Modified VDA-275 (μg/g) GB Test T_(m) = 185° C. T_(m) = 205° C.T_(m) = 215° C. (μg/g) Control 11 1.80 3.30 4.00 3.5 Control 12 4.707.90 13.60 3.43 Sample 57 0.26 0.8 1.47 0.39 Sample 58 0.40 0.70 0.940.40 Sample 59 0.35 0.76 1.58 0.067 Sample 60 0.7 0.86 1.10 0.084 Sample61 0.63 2.60 11.00 1.13 Sample 62 1.26 2 4.16 3.18 Sample 63 0.67 1.365.33 0.232 Sample 64 0.88 1.26 4.27 0.367

The above results demonstrate the synergistic emission reduction ofethylene urea in combination with benzoguanimine and/or allantoin. Theeffect is especially dramatic at higher temperatures.

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention sofurther described in such appended claims.

1.-20. (canceled)
 21. A polymer composition comprising: apolyoxymethylene polymer; and a formaldehyde stabilizer package forreducing formaldehyde emissions, the formaldehyde stabilizer packagecomprising a blend of emission control agents, the blend including asubstituted hydantoin and at least one emission control agent selectedfrom a guanamine compound, a hydantoin, an amino acid, and an ethyleneurea.
 22. A polymer composition as defined in claim 21, wherein theformaldehyde stabilizer package comprises a blend of a guanaminecompound and a substituted hydantoin, the substituted hydantoincomprising allantoin.
 23. A polymer composition as defined in claim 21,wherein the formaldehyde stabilizer package comprises a blend of asubstituted hydantoin and a hydantoin.
 24. A polymer composition asdefined in claim 21, wherein the formaldehyde stabilizer packagecomprises a blend of a substituted hydantoin and an amino acid.
 25. Apolymer composition as defined in claim 24, wherein the amino acidcomprises arginine.
 26. A polymer composition as defined in claim 22,wherein the substituted hydantoin is present in an amount less thanabout 0.5% by weight and in an amount greater than about 0.001% byweight.
 27. A polymer composition as defined in claim 22, wherein theguanamine compound comprises benzoguanamine.
 28. A polymer compositionas defined in claim 22, wherein the guanamine compound is present inrelation to the other emission control agent at a weight ratio of fromabout 20:1 to about 2:1.
 29. A polymer composition as defined in claim22, wherein the guanamine compound is present in the composition in anamount greater than about 0.2% by weight and being present in an amountless than about 2% by weight.
 30. A polymer composition as defined inclaim 21, wherein the formaldehyde stabilizer package comprises anethylene urea.
 31. A polymer composition as defined in claim 30, whereinthe ethylene urea is present in an amount from about 0.001% by weight toabout 5% by weight.
 32. A polymer composition as defined in claim 21,wherein the polymer composition exhibits a formaldehyde emission of lessthan about 5 ppm when tested according to VDA Test
 275. 33. A polymercomposition as defined in claim 21, wherein the polymer compositionexhibits a formaldehyde emission of less than about 4 ppm when testedaccording to VDA Test
 275. 34. A polymer composition as defined in claim21, wherein the polymer composition exhibits a formaldehyde emission ofless than about 3 ppm when tested according to VDA Test
 275. 35. Apolymer composition as defined in claim 21, wherein the polymercomposition further contains a nucleant in an amount from about 0.05% byweight to about 1% by weight, an antioxidant in an amount from about0.05% to about 2% by weight, and a lubricant in an amount from about0.05% to about 1.5% by weight.
 36. A polymer composition as defined inclaim 22, wherein the guanamine compound is present in the polymercomposition in an amount from about 0.3% to about 0.8% by weight andwherein the substituted hydantoin is present in the polymer compositionin an amount from about 0.01% to about 0.3% by weight.
 37. A polymercomposition as defined in claim 21, wherein the polymer composition hasa tensile modulus of at least 1200 MPa when tested according to ISO Test527 at 23° C., has a tensile strain at yield of greater than about 7%when tested according to ISO Test 527 at 23° C. and has a notched Charpyimpact strength of greater than about 3 kJ/m² when tested according toISO Test 179-1 at 23° C.
 38. A molded article made from a polymercomposition of claim
 21. 39. A molded article as defined in claim 38,wherein the molded article comprises a medical product.
 40. A moldedarticle as defined in claim 39, wherein the medical product comprises aninhaler or an injector.